Electron device



Dec. 24, 1940. BRUCHE ELECTRON DEVICE Filed May 21, 1938 POM El? ZASUPPLY POWER Zf/ SUPPLY INVENTOR. 7K $T ERUC/IE ATTORNEY.

Patented Dec. 24, 1940 UNITED STATES ELECTRON DEVICE Ernst Bruche,Berlin-Reinickendorf, Germany,

assignor to General Electric Company, a corporation of New YorkApplication May 21, 1938, Serial No. 209,157 In Germany May 31, 1937 2Claims.

This invention relates to electron devices, and more particularly, tomethod and means of focusing electrons to overcome spherical aberration.

More particularly, the invention concerns itself with providing anelectron lens system in which an apertured diaphragm is provided, whichdiaphragm is so shaped to avoid distorting the electrostatic fieldscomprising the electron lens.

In the prior art electrostatic electron lenses ill have made use ofcylindrical electrodes in which one or more apertures might be provided.The apertures were provided in planar diaphragms and accordingly, wheretwo such electrodes were placed in proximity to each other and hadpoten- 15 tials applied thereto to provide the electrostatic field whichserves as the electron lens, considerable distortion of the lines offorce of this electrostatic field was produced. Accordingly, such anelectrode system introduces distortions in the 20 focusing of electronswhich are analogous to spherical and chromatic aberrations, as Well ascoma in optical systems.

According to my invention, this is overcome by shaping the apertureddiaphragms so that no 25 distortion of the electrostatic fields isproduced. To this end, the diaphragm is shaped to have the same form asthe electrostatic field in which the diaphragm is immersed so that thelines of force of the electrostatic field are co-incident with the 30diaphragm itself. Under such circumstances no distortion is introduced,and accordingly, electrons may be focused free from the above namedaberrations and distortion.

Accordingly, the main object of my invention 35 is to provide animproved electron optical system.

A further object of my invention is to provide an electron opticalsystem in which electrodes have non-planar diaphragms.

A still further object of my invention is to pro- 40 vide electrodestructures for electron optical systems in which the diaphragms areshaped to coincide with the electrostatic fields which focus theelectrons.

A still further object is to provide electrode 45 structures havingdiaphragms in which the diaphragm has the same shape as anequi-potential electrostatic surface.

Other objects of my invention will become apparent from reading thedescription in conjunc- 5 tion with the drawing.

In describing my invention in detail, reference will be made to thedrawing, in which Fig. 1 shows an electrode system for purposes ofexplaining the invention, While Figs. 2 and 3 show one embodiment of myinvention in which a non-planar apertured diaphragm coinciding with anequi-potential electrostatic surface is provided.

In Fig. 1 I have shown a cathode ray tube I l in which is positioned anelectron gun comprising 5 an indirectly heated cathode, a focusing orcontrol electrode 3, a first anode 5, a second anode 1, and aluminescent screen 9. A source of potential 2! supplies potentials tothe various electrodes through a voltage divider 23. Due to thedifference in potential supplied to the electrodes 5 and l,electrostatic fields will be set up between these two electrodes whichwill result in equi-potential surfaces of approximately spherical formas shown by the dotted lines in Fig. 1. If, for example, it was desiredto place a diaphragm at the end of the electrode 5 with an aperturetherein in order to restrict the ray for producing finer focus, theintroduction of a planar diaphragm would change the distribution of theelectrostatic lines of force so that there would result instead ofspherical equi-potential surfaces equi-potential surfaces having adistorted formdifferent from those of a sphere. Accordingly, theelectrons from the cathode I would not be focused upon the targetelectrode 9 properly. However, by making the diaphragm spherical in formsuch as shown in Fig. 2 where the diaphragm I9 is approximatelyspherical in shape, no distortion of the equi-potential surfaces takesplace, and accordingly, the electrons pass through a plurality ofsubstantially spherical equi-potential surfaces close to an axis ofsymmetry. Under such conditions, there is, in effect, provided acorrected electron optical lens which is free from spherical andchromatic aberrations, as well as coma.

In Fig. 2, I have shown a further electrode l3 provided in the form ofan electrical conducting surface mounted on the wall of the envelope ll.Where it is desired to use a different configuration of the electrodesl5 and I such that the equipotential surfaces would have a differentform than those of spheres, then the diaphragm l9 may take on adifferent form. For example, if the equi-potential surfaces areparabolic in form, then 5 the diaphragm l9 instead of being a sphericalsurface of revolution would be a parabolic surface. Or if ellipticalequi-potential surfaces are provided, then the diaphragm l 9 is madeelliptical in shape.

In other words, the diaphragm takes the shape of the electrostatic fieldwhich would be provided in the absence of the diaphragm. Under suchconditions, there is no deformation of the potential field and theelectrons are actually focused upon the luminescent screen.

Under such conditions where it is desirable that the aperture in IQconstitute the object plane, an image of which is to be focused upon afluorescent screen or target electrode, then the potentials may besuitably varied such that the aperture shall lie in the object plane andfurther electrodes may be positioned intermediate the diaphragm l9 andthe screen 9 to provide an optical system producing an image of theaperture in l9 on the screen 9.

Having described my invention, what I claim is:

1. An electron lens comprising a first cylindrical electrode, a secondcylindrical electrode partially surrounding one end of the firstcylindrical electrode, and a spherical apertured diaphragm substantiallyclosing the surrounded end of the first cylindrical electrode saiddiaphragm extending within the surrounded end of said first cylindricalelectrode.

2. In a cathode ray tube, an electron lens comprising a firstcylindrical electrode, a second cylindrical electrode surrounding oneend of the first cylindrical electrode, both of said electrodes beingadapted to set up in the region of the surrounded electrode, anelectrostatic field having a predetermined form of equi-potentialsurfaces, and a non-planar apertured diaphragm substantially closing thesurrounded end of said first cylindrical electrode and extending withinthe first cylindrical electrode having its surface congruent with one ofthe said predetermined equi-potential surfaces whereby the aberrationsof the lens are reduced.

ERNST BRUCHE.

